The ubiquitous use of chlorine as a disinfectant in public water supplies has introduced a subtle health hazard of its own. Chlorine has been shown to react with humic substances present in such waters to produce trihalomethanes (THM) such as chloroform. The Environmental Protection Agency has identified trihalomethanes as carcinogens in animals, and has published a maximum contaminant level of 0.10 mg/liter (100 ppb) for total THM in community water systems (National Interim Primary Drinking Water Regulations; Control of Trihalomethanes in Drinking Water; Final Rules. U.S. Environmental Protection Agency, Federal Register, Vol. 44, No. 231, Nov. 29, 1979).
Attempts at removing trihalomethanes from chlorinated drinking water have met with but limited success. If THM is removed, but residual chlorine and humic substances remain, the THM will re-form. If the active chlorine is removed, as with granular activated charcoal, the water must be re-chlorinated to meet standards, and THM again may re-form.
An alternative approach is to remove the humic substances that are THM precursors. These substances, generally weak acids, are found in many natural waters, are probably leached from organic materials found in soil, and are usually found at high concentrations in surface waters, and at lower concentrations in most ground waters. Materials that previously have been used for removing them from water include adsorbents such as granular activated carbon, coagulants such as alum and ferric sulfate, and conventional ion exchange resins, including both strongly and weakly basic anion exchange resins. With strongly basic resins the affinity for these humic substances is so strong that regeneration of the resin is frequently a problem.
Each of these processes shares the problem that relatively large amounts of treating agents must be added to the drinking water to effectively reduce the THM precursor levels to below permissible limits. In addition, each possesses additional problems of its own, some of which are described above.
Accordingly, an object of the present invention is to minimize the amount of treating agent that must be added to water to significantly reduce its THM precursor content. Another object is to remove THM precursors in a way that does not interfere with conventional drinking water disinfectant processes. Additional objects will become apparent upon consideration of the following disclosure.